For the past 25 years, surfboard riding and associated wave riding activities, e.g., knee-boarding, body or "Boogie" boarding, skim-boarding, surf-kayaking, inflatable riding, and body surfing (all hereinafter collectively referred to as wave-riding) have continued to grow in popularity along the world's surf endowed coastal shorelines. In concurrence, the 80's decade has witnessed phenomenal growth in the participatory family water recreation facility, i.e., the waterpark. Large pools with manufactured waves have been an integral component in such waterparks. Several classes of wavepools have successfully evolved. The most popular class is that which enables swimmers or inner-tube/inflatable mat riders to bob and float on the undulating unbroken swells generated by the wave apparatus. Although small breaking waves can result from this class of wavepool, it is not an ideal wave for wave-riding. A few pools exist that provide large turbulent white-water bores that surge from deep to shallow pool end. Such pools enable white water bore (broken wave) riding, however, broken wave riding is not preferred by the cognoscenti of the wave-riding world. The type wave which holds ultimate appeal to a wave-rider is a combination of unbroken yet rideable wave face with a "breaking"/"transitioning" curl or spill.
The ideal unbroken yet rideable wave face can be described as a smooth inclined mound of water of at least one meter in height with a face of sufficient incline such that the gravity force component can allow a rider to overcome the forces of drag and perform water skimming (e.g., surfing) maneuvers thereon. The classic breaking wave can be described as one moving obliquely incident to a beach; having a wave height in excess of one meter; having a portion closest to the beach that is broken, while that portion furthest from the beach has a smooth surface; having the transition from the smooth to the broken part of the wave occurring continuously over a region spanning a few wave heights; and having a transition area with a duration in excess of 10 seconds. In breaking wave, this transition area is of particular interest to the wave-rider. The transition area is where the wave-rider performs optimum water skimming (e.g., surfing) maneuvers. The transition area is also where the wave face reaches its maximum angle of steepness.
As a wave-rider develops in skill from beginner to advanced, he or she will seek mastery upon different types of waves. First timers start on the "inside" with an already broken white water bore. These waves are the easiest to catch, however, they offer little opportunity for surfing maneuvers. The next step is to move to the "outside," just past the break zone. Mere a beginner prefers an unbroken wave with only enough steepness to allow them to "catch" the wave. As the wave breaks, beginners prefer a gentle spilling type wave. The more advanced a wave-rider becomes the greater is the preference for steeper waves, with an ultimate wave shape resembling a progressive tube or tunnel.
For years, inventors have attempted to mechanically duplicate the ideal wave for wave-riding that will offer the complete range of wave-riding experience for beginners and advanced riders alike. The majority of such attempts focus on reproduction of travelling, progressive gravity waves found naturally occurring at a beach. Unfortunately, such attempts have met with limited success for wave-riding. Problems inherent to travelling progressive wave technology include: safety, skill, cost, size and capacity. Reproduction of travelling, progressive breaking waves require a large pool with expensive wave generating equipment. Desired increases in wave size result in inherently more dangerous conditions, e.g., deeper water and strong currents. Access to travelling progressive waves usually requires a strenuous swim or paddle through broken waves in order to properly position oneself in the unbroken wave "take-off zone." Catching a progressive breaking wave requires split-second timing and developed musculature. Riding a progressive breaking wave requires extensive skill in balancing the hydrodynamic lift forces associated with a planing body and the buoyancy forces associated with a displacement body. Progressive waves are an inherently low capacity attraction for water parks, i.e., one or two riders per wave. As a consequence of limited wave quality, inordinate participant skill, excessive cost, potential liability, and large surface area to low rider capacity ratios, wavepools specifically designed to produce conventional travelling progressive breaking waves have proven, with few exceptions, unjustifiable in commercial application.
Le Mehaute (U.S. Pat. No. 3,802,697) and the following three publications: (1) Hornung, H. G. and Killen, P., "A Stationary Oblique Breaking Wave For Laboratory Testing Of Surfboards," Journal of Fluid Mechanics (1976), Vol. 78, Part 3, pages 459-484; (2) P.D. Killen, "Model Studies Of A Wave Riding Facility," 7th Australasian Hydraulics and Fluid Mechanics Conference, Brisbane, (1980); and (3) P. D. Killen and R. J. Stalker, "A Facility For Wave Riding Research," Eighth Australasian Fluid Mechanics Conference, University of Newcastle, N.S.W. (1983), (all three articles will be collectively referred to as "Killen") describe the production of a unique class of progressive waves called a stationary wave. Stationary waves, as opposed to the aforementioned travelling waves, are normally found in rivers where submerged boulders act to disturb the flowing river water, creating a wave which advances against the current at an equal and opposite speed to remain stationary relative to the bottom.
The stationary breaking waves as contemplated by Le Mehaute and Killen avoid the "moving target" problem associated with travelling progressive gravity waves. Consequently, from a shore bound observer's perspective, they are more predictable, easier to observe, and easier to access. Although improved, the stationary breaking waves of Le Mehaute and Killen when applied to the commercial water recreation setting are still plagued by significant progressive wave problems. In particular these problems include: inordinate rider skill to catch and ride the wave, deep water drowning potential (since the water depth is greater than the height of the breaking wave) and high costs associated with powering the requisite flow of water to form the wave. In other words, both Le Mehaute and Killen still contemplate relatively deep bodies of water comparable to that found at the ocean shore.
Furthermore, the wave forming process of Le Mehaute and Killen involves an obstacle placed in a flow of water bounded by containment walls. The hydraulic state of the flow is described as supercritical flow going up the face of the obstacle, critical flow at the top or crest of the obstacle as the wave breaks (a towering "hydraulic jump"), and subcritical flow over the back of the obstacle. A submerged dividing stream surface splits the supercritical upstream portion from the subcritical downstream portion which flows over the back of their respective obstacles. A corollary to this "critical flow" breaking process (i.e., where the Froude number equals one at the point of break) is the relationship of water depth with wave size, wherein the maximum wave height obtainable is 4/5 the water depth. Consequently, in Killen and Le Mehaute, the larger the desired wave the deeper the associated flow.
The above-described disadvantage has enormous economic significance. Killen and Le Mehaute require pumps with enormous pumping capacity to produce a larger sized wave. Furthermore, a rider's performance under a deep flow condition requires great skill.
By way of example, when a wave-rider paddles to catch a wave in a deep water flow (a deep water flow is where the pressure disturbance due to the rider and his vehicle is not influenced by the proximity of the bottom) his vehicle serves primarily as a displacement hull sustained by the buoyancy force and transitions to primarily a planing hull (reducing the draft of the board) as a result of the hydrodynamic lift that occurs from paddling and upon riding the wave. The forces involved in riding this wave is a combination of buoyancy and hydrodynamic lift. The faster the board goes the more the lift is supporting the weight of the rider and the less the buoyancy force. In reaction to this lift, there is an increase in pressure directly underneath the board. This pressure disturbance diminishes at a distance from the board in ratio to one over the square of the distance.
In a deep water flow environment, by the time the pressure disturbance reaches the flow bed, it has already attenuated to such a low level that the bottom creates a negligible influence on that pressure disturbance. Consequently, there is no reaction to be transferred to the rider. This lack of bottom reaction in a deep water flow leaves a rider with no support. Lack of support results in greater physical strength required to paddle, and to transition the surfboard from a displacement hull to a planing hull, in order to catch the wave. Lack of support also results in greater instabilities with axiomatic greater skill required to ride the wave.
Furthermore, a deep water flow has inherently increased drowning potential. For example, a 2 foot high-breaking wave requires a 5.38 knot current in 2.5 feet of water. Not even an Olympic swimmer could avoid being swept away in such current.
Frenzl (U.S. Pat. Nos. 3,598,402 (1971), 4,564,190 (1986) and 4,905,987 (1990)) describes water flow up an incline. However, in addition to the above-described disadvantages, the structure of Frenzl is described as the bottom of a container. The side walls of this container function to constrain the water flow in its upward trajectory in expectation of conserving maximum potential energy for subsequent recirculation efficiency. However, it has been found that such side walls propagate oblique waves which can interfere with the formation of supercritical flow and eliminate the possibility of breaking waves. That is, the container of Frenzl simply fills with water and submerges any supercritical flow. The side wall containment also proves detrimental in its ability to facilitate ride access. Further, Frenzl's device is designed for wave riding in equilibrium. The majority of wave riding maneuvers, however, require movement or oscillation around a point of equilibrium through the various zones of inequilibrium, in order to achieve maneuvers of interest.